High-frequency longitudinal and transverse dynamics in water.
High-frequency longitudinal and transverse dynamics in water.
复制标题
水中的高频纵向和横向动力学。
DOI：
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发表时间：
2005
期刊：
影响因子：
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通讯作者：
G. Ruocco
中科院分区：
文献类型：
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作者：
E. Pontecorvo;Michael Krisch;A. Cunsolo;G. Monaco;A. Mermet;R. Verbeni;F. Sette;G. Ruocco
在明显不同的热力学条件下（T=263-420 K，在或接近环境压力下，P=2 kbar），对4至30 nm（-1）之间的波矢量Q进行了液态水动态结构因子S （Q, ω）的高分辨率、非弹性x射线散射测量。与先前的非弹性x射线和中子研究一致，证实存在两种非弹性贡献（一种与Q色散，另一种几乎非色散）。它们的温度和Q依赖关系的研究为结构松弛过程控制液态水动力学提供了强有力的支持。结合纵向动力学对Q -频散模式进行粘弹性分析，发现声速经历了从绝热声速（c(0)）（粘性极限）到无限频声速（c(∞)）（弹性极限）的完全过渡。在减小Q时，当从弹性侧接近过渡区时，我们观察到第二个弱色散特征的强度降低，当达到粘性区时，该特征完全消失。这些发现明确地确定了第二个激励是具有纵向对称分量的横向动力学的特征，一旦离开纯粘性状态，就可以在S （Q, ω）中看到。
High-resolution, inelastic x-ray scattering measurements of the dynamic structure factor S (Q,omega) of liquid water have been performed for wave vectors Q between 4 and 30 nm(-1) in distinctly different thermodynamic conditions ( T=263-420 K ; at, or close to, ambient pressure and at P=2 kbar ). In agreement with previous inelastic x-ray and neutron studies, the presence of two inelastic contributions (one dispersing with Q and the other almost nondispersive) is confirmed. The study of their temperature and Q dependence provides strong support for a dynamics of liquid water controlled by the structural relaxation process. A viscoelastic analysis of the Q -dispersing mode, associated with the longitudinal dynamics, reveals that the sound velocity undergoes a complete transition from the adiabatic sound velocity ( c(0) ) (viscous limit) to the infinite-frequency sound velocity ( c(infinity) ) (elastic limit). On decreasing Q , as the transition regime is approached from the elastic side, we observe a decrease of the intensity of the second, weakly dispersing feature, which completely disappears when the viscous regime is reached. These findings unambiguously identify the second excitation to be a signature of the transverse dynamics with a longitudinal symmetry component, which becomes visible in S (Q,omega) as soon as the purely viscous regime is left.